Porous metal article



Gd. 15, 1945. J, RVI r 2,409,295

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Filed Dec. 8. 1941 2 Sheets-Sheet 2 l I I I I I I I I I '1 I, I J' I!I/I/IIIIII 1/,

THUR ATI'ORN Patented Oct. 15, 1946 POROUS METAL ARTICLE John '1. Marvinand Roland R-Koehrlng, Dayton, Ohio, assignors to General MotorsCorporation, Detroit, Mich, a corporation of Dela- Ware ApplicationDecember 8, 1941, Serial No. 422,138

3 claims. 1

This invention relates to porous metal articles and is particularlyconcerned with the surface treatment of such articles for providingcharacteristics on the entire porous surface of the articles making themsuitable for specific uses.

An object of the invention is to provide a method whereby porous metalarticles may have their entire porous surface plated with another metalwhich gives more desirable characteristics to the article.

Another object of the invention is to provide a method for coating, orplating, the entire surface of the porous metal article with anothermetal wherein the porous metal article may be made from an inexpensivematerial and have a thin plate of inexpensive metal thereover wherebythe character of the plated metal is imparted to the porous metalsurface thereby reducing the cost of manufacture of the specificarticle.

Another object of the invention is to provide a method for plating thesurface of the porous metal articles by deposition wherein the positionof the metals in the electro-chemical series is utilized.

A further object of the invention is to provide a method for coating thesurface of a porous metal article with another metal which is capable ofbeing vaporized or sublimed and then deposited on the surface ofv theporous metal article and diffused to some extent into the porous metalarticle if desired.

In carrying out the above objects it is a further object of theinvention to provide a method wherein the entiresurface of the porousmetal article is plated or coated by means of expedients wherein theplating or coating metal in suitable form is caused to pass through theporous metal article whereby every surface of each pore is coated orplated.

Another object of the invention is to provide a new article ofmanufacture which consists of a matrix of one metal coated completelythereover with another metal whereby the second metal imparts itscharacteristics to the surface of the article.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings wherein preferred embodiments of one form of the presentinvention is clearly shown.

In the drawings:

Fig. 1 is a diagrammatic view, shown in section, showing an apparatusused in the plating of porous metal articles by deposition.

Fig. 2 is a view taken on the line 22 of Fig. Fig. 3 is a fragmentaryand greatly enlarge sectional view of the porous metal article aftertreatment of the apparatus shown in Fig. 1.

Fig. 4 is a view of another type of apparatus used in the treatment ofthe metal article with metal vapors.

Fig. 5 is a view taken on the line 5-5 of Fig. 4.

Fig. 6 is a fragmentary viewon a greatly enlarged scale taken throughline 6-6 of Fig. 5.

Porous metal articles due to their relatively large surface are in manycases attacked by oxidizing fluids such as water, air containingmoisture, and the like. It has been found, for example, that porous ironis more readily oxidized in the atmosphere than is solid iron made byconventional practice. This may be explained by the fact that porousiron presents a relatively greater surface area per unit volume thandoes iron made by conventional practices. For this reason, it is oftenhighly desirable to protect such articles whether they be made fromporous iron or other porous metals which are attacked by the air orfluids which may pass therethrough. For example, porous bronzes, porousferrous alloys, porous nickel alloys, porous aluminum alloys and thelike may, by surface treatment, all be improved for certain intendeduses thereof wherein the surface treatment provides a protective film orlayer. It should be understood, however, in many instances the intendeduse of the article has no deleterious effect thereon and such surfacetreatments are therefore unnecessary.

Further .it is often possible by using surface treatment to reduce thecost of the manufacture of the part. For example, in some cases a porouscopper alloy part may be highly desirable from an oxidation standpointbut due to the cost such a part may not be economical. By utilizing theinvention described herein it is possible to provide a ferrous part andthen plate the entire surface thereof with copper thereby reducing thecost of the part and making the use thereof economical while the surfacehas all of the characteristics of copper due to the copper platethereon. Thus it will be apparent that there are many commercial usesfor the present invention.

The problems present in plating or coating of the porous metal parts aremany due to the large surface areas and the tortuous, serpentine pathsof the pores. Such porous articles do not lend themselves toelectroplating'since the throwing power of the electrolyte does notpenetrate to any great depth and gassing at the adjacent surfaces of-thepores also prevents a uniform electrodeposition.

Electrochemical deposition by the utilization of salt solutions ofvarious metals has not heretofore been satisfactory since by the timethe salt solution passes through the interstices of the porous metalarticle, the salt of the metal in solution has been depositioned outadjacent the external surfaces of the porous metal article and thereforeinsufficient metal remains in the salt solution to accomplishsatisfactory deposition and plating. In the present invention we proposeto cause a metal salt solution to flow through porous metal articles ata sufiicient rate to providefor adequate surface plating of the entire.porous surface. To this end an apparatus 20 may be employed wherein aplurality of porous metal plates 22,'for example, are held in a fixture24 which fixture is clamped between two members 26 and 28 by means ofclamps 30. The member 26 is substantially conical and is connected to apipe 32 which leads from a pump which issupplied through pipe 38 from asalt solution tank 88 containing a salt solution 40. Salt solution 40 isforced by pump 34 into member .26 and through porous. metal article 22whence it enters member 28 and passes bygravity therefrom through pipe42 back into the tank 38. Thus continual circulation of the saltsolution through the. porous metal articles may be accomplished andconcentration of the metal in the salt solution may be closelycontrolled to keep the concentration at a substantially uniform figure.After a suitable time, which is best determined by examination of theporous article, it will be found that the entire porous surface thereofwill be plated with the metal in the salt solution. After making a trialrun it is then pos- 54 on a suitable hearth ll. The furnace is like-'wise preferably includes a water cooled baflie chamber 82 or condenserwhich may be connected to an exhaustblower 84 if insumcient flow isexperienced. I In the use of the apparatus, the

a metal in pan 50, for example'cadmium, is heated sible to producearticles without further ex amination by maintaining the flow of saltsolution therethrough for a predetermined time period. A number ofarticles 22 may be treated at the same time. The articles, for example,are porous iron and the salt solution may be copper sulphate, since itis possible to coat copper directly on the iron. Likewise, by referringto the electrochemical series it is possible to choose various saltsolutions which will deposit their metal upon another metal in thearticle to be plated. Thus, any metal in the electrochemical series maybe coated with any metal found lower in the same series due to the factthat as onereads downwardly in the series the rate of ease, of reductionincreases, or stated differently, the metals in the series .readingdownwardly increase in activity as oxidizing agents, such phenomenonbeing well known in electrochemistry. It should be understood that afterthe solution is contaminated with the metal being replaced to asuificient degree, which is also best determined by trial, it shouldeither be purified by any well known method, or replaced. I

Fig. 3 shows a portion of the porous metal article after plating wherein44 indicates the matrix portion, or in the present case, the porousiron, and. 46 indicates the copper plating thereover.

In many instances it may be desirable to partially diffuse the platingmetallurgically into the matrix after treatment which may beaccomplished by suitable heat treatment. However, for most purposes theplating is sufficient.

above its boiling point and vaporized and is drawn by blower 84 throughthe furnace and likewise-through the porous metal articles II. In orderto provide sufficient atmosphere within the furnace it may be necessaryin some cases to include a non-oxidizing or reducing atmosphere whichmay be admitted through the pipe 68 in limited amouts and which may beused as a carrier for a metallic vapor. It is desirable to maintain thefurnace portion in which the porous metal articles are disposed at atemperature but slightly above the boiling point of the metal beingvaporized and this may be accomplished by utilizing a suitable heatingmeans. After the atmosphere containing the metallic vapor has passedthrough the furnace and entered the chamber 82 it is cooled below theboiling point whereby the metal is condensed within the chamberdand maybe recovered periodically and reuse In the present instance the coatingof cadmium, zinc, etc., which depositson the porous metal articles maybe completely or partially difl'used therein by use of suitable heattreatment and maintenance thereof during or after the coating operationhas been completed. In many instances this diffusion is not requiredalthough it should be understood that such diffusion may be accomplishedif desired.

From the foregoing it is manifest that we have provided a method forcoating or plating the entire surface of porous metal articles withanother metal which metal acts to change the characteristics of thesurface of the porous metal articles for specific purposes and uses. Inthis manner, non-corrosive surfaces may be deposited on porous metalarticles or surfaces having desired physica1 and/or chemicalcharacteristics. The method is inexpensive and easy to accom- Plish.

While the embodiments of the present invention as herein disclosed,constitute preferred forms, it is to be understood that other formsmight be adopted, all coming within the scope of the claims whichfollow.

What is claimed is as follows:

1. A method of coating the entire porous surface of a porous metalarticle having pores passing completely through the article with a metallower in the electrochemical series than the metal of thearticle'andwherein the coating is metallurgically bonded to the surfaceof the article, the

0 steps comprising; continuously circulating solely There are severalmetals which may be easily vaporized, such as cadmium, zinc, selenium,etc. These metals often provide a very desirable suring the article at atemperature below the melting point of the coating metal for a timesumcient to cause at least partial metallurgical difiusion of thecoating metal into the metal of the article whereby the surfacecharacteristics of the porous metal article are those of the metaldeposited on the surfaces of the walls of the pores without destroyingthe porosity. of the article.

2. A method of coating the entire porous surface of a porous metalarticle with another metal which is below the metal oi the article inthe electrochemical series and wherein the pores of said article passcompletely therethrough, the step of circulating an electrolytecontaining the metal to be deposited on the surface of the porous metalarticle through said pores or said porous metal article through pumpingand for a time sufiicient to cause the metal in said electrolyte todeposit to a desired thickness upon the entire porous surface of thearticle to be coated whereby the surface characteristics of the porousmetal article are those of the metal deposited on the sur faces of thewalls of the pores without destroying the porosity of the article,

3. The method as claimed in claim 2 including the added step of heatingthe coated article to a temperature and for a time sumeient to cause atleast partial metallurgical difiusion of the coating metal into themetal of the article.

- JOI-m T. MARVIN.

ROLAND P, KQELEING.

